Processing AIDS for recycled plastics
Different from new materials, plastic recycled materials often have more defects, such as processing properties, mechanical properties, appearance and color, aging resistance and so on, which affect the application of plastic recycled materials. In order to minimize the defect effect of recycled materials, it is often necessary to add plastic additives.
1, the role of plastic additives
Plastic additives can effectively improve the processing performance of recycled materials and improve production efficiency; And it can improve the physical and mechanical properties and service performance of recycled material products, improve its service value and working life, and achieve the purpose of high value of recycled material.
There are many types of plastic additives, which play different roles. They can be understood by referring to the following table:
2. Requirements for additives
Because the processing of plastic and the use of products are affected by many factors, so the requirements for the selection of additives will be very high, mainly the following points:
1. It should have good compatibility with the synthetic resin to be added, and be stable for a long time and evenly dispersed in the resin;
2. Synergistic effect. Try to use plastic auxiliaries that can promote the function of each other;
3. Good durability. Does not exudate, develop, migrate or be extracted by water or liquid substances;
4. suitable for the use of products;
5.Better adaptability to processing conditions;
Good dispersity, easy to disperse evenly in the process of processing and forming.
The above points can meet the requirements of most recycled materials for additives, plastic additives can achieve these points will play a role, so that the performance of recycled plastics is improved.
3, commonly used several plastic additives
1. Characteristic additives
The main function of such additives is to give plastic products some characteristics, such as physical and mechanical properties, flexibility, flame retardant and so on.
1) plasticizer
Plasticizer can reduce the melt temperature of plastic, viscosity and hardness, increase the softness of plastic fluidity and products and cold resistance, improve the processing performance of plastic and use performance thereby.
Plasticizer basically is used at PVC, cellulose derivative, synthetic rubber and in the plastic such as nylon, not all plastics need plasticizer, among them about 80% plasticizer is used at PVC in.
(2) the filler
Is to add an inert material to the plastic, the purpose is to increase quality, reduce cost, etc. Fillers can also improve the processing properties of plastics and some use properties, such as improving strength, heat resistance and corrosion resistance.
Fillers are generally powder materials, the main varieties are calcium carbonate, talcum powder, kaolin, wollastonite, mica and wood powder, etc., often used in PVC, polyolefin and ABS resin.
(3) strengthening agent
Reinforcer can significantly improve the strength of recycled material products, the vast majority of them are high strength, fibrous inert substances, such as glass fiber, carbon fiber, asbestos, etc., glass fiber dosage is large.
Reinforcers are now widely used in PVC, PP, PE, nylon and other plastics.
(4) colorant and fluorescent whitening agent
Coloring agent is mainly to give plastic color, make the product become more beautiful. Fluorescent whitening agent can effectively improve the appearance of recycled plastic products, and can be used with colorants to make products more beautiful color.
(5) flame retardants
Flame retardants are additives that prevent or slow the burning of plastics. It can be divided into two categories: additive flame retardants and reactive flame retardants. Additive flame retardants are usually added to the base resin, and they are simply physically mixed with the resin. Reactive flame retardants is commonly intramolecular monomer containing flame retardant elements and reactive groups, such as halogen acid anhydride, halogenated bisphenol a and phosphorus polyols, etc., because of the reactivity, can be chemically bonded to the resin molecular chain, become a part of the plastic resin, the most reactive flame retardant structure or synthetic additive flame retardant monomer.
⑥ Impact modifier
Additives that can improve the impact strength of plastics are called impact modifiers. Generally for some elastomers and good toughness of plastic, mainly used in PVC, PS, PP and some engineering plastics.
All landowners foaming agent
Foaming agent can produce gas namely, make plastic goods produces the material of bubble hole or gap, cent is physical foaming agent and chemical foaming agent. Physical foaming agents generally rely on the change of their physical state to release gas, mostly volatile liquid substances, hydrochlorofluorocarbons (such as freon), low alkanes (such as pentane) and compressed gas are the representatives of physical foaming agents. Chemical foaming agent is based on the gas released by chemical decomposition for foaming, commonly used hydrazine derivatives, the most important one is azodicarbonamide, can be used in PVC, PE, PS, PP, ABS and other plastics.
2. Stabilizer
The main function of stabilizers is to delay or stop the degradation of plastics by physical (heat, light) and chemical (oxygen, microbial) factors. There are heat stabilizer, light stabilizer and antioxidant agent.
① Heat stabilizer
Heat stabilizer can delay or avoid damage and further degradation of plastics due to heat action. Usually not specified, heat stabilizer refers to the use of PVC and PVC copolymer processing stabilizer. Polyvinyl chloride and vinyl chloride copolymer are thermally sensitive resins, which are easy to release hydrogen chloride during thermal processing, and then lead to thermal degradation reaction. Thermal stabilizers widely used in industry generally include basic lead salts, metal soaps, organic tin, organic antimony and other main stabilizers and epoxy compounds, phosphite esters, polyols, diketones and other organic auxiliary stabilizers.
② Light stabilizer
Light stabilizers mainly inhibit or weaken the photodegradation of plastics and improve the weather resistance of plastics. In addition, impurities or chromophores in polymers can also promote photooxidation degradation of polymers.
Light stabilizer is mainly used for polyolefin, followed by rubber modified PS, PVC, PU and so on.
③ Antioxidants
Antioxidants can delay or inhibit the oxidative degradation of plastics. Antioxidant is the most important type of stabilizer for plastics, and almost all polymer resins are involved in the application of antioxidant.
Generally divided into primary antioxidants and auxiliary antioxidants. The main antioxidant is to capture polymer peroxide free radicals as the main function; Auxiliary antioxidants have the function of breaking down polymer peroxide compounds, also known as "peroxide decomposers".
3. Processing additives
Processing additives can make plastic recycled materials easy to shape or improve the molding efficiency, mainly including release agent, lubricant and so on.
1) lubricants
Lubricants can reduce the viscosity of plastic melt or the friction coefficient between melt and processing equipment, which can be divided into internal lubricants and external lubricants. Internal lubricant can reduce the polymer viscosity and energy consumption by reducing the friction between polymer molecules. The role of external lubricants is to reduce friction or adhesion between polymers and processing equipment. External lubricants are usually incompatible with polymers.
(2) release agent
Similar to an external lubricant, a thin layer of isolator is formed between the product and the die to enable the product to self-release from the die.
4. Development prospect of plastic additives
With the development of plastic products industry, plastic additives as an indispensable component of general plastics engineering, engineering plastics high performance and the key of synthetic resin modification to achieve functionalization, plastic additives industry is also developing in the direction of large-scale and intensive. The application field of plastic processing auxiliaries will continue to expand, and the product variety will also develop towards multi-functional, compound and special type. The development and production of high-performance green, environmental protection and plastic additives will become the main direction of the development of China's plastic additives industry in the future.
(Source: fengj.com)
